The overall objective of the proposed research is to define specific mechanisms underlying the pathophysiology of cyclosporine A nephrotoxicity, with particular emphasis on the study of changes in renal blood flow, autoregulation of blood flow, and intrarenal distribution of blood flow. These areas are of particular importance because of the strong implications of a vascular origin for the toxic changes induced by cycloporine. In addition, the sympathetic and hormonal influences which may modulate the vascular changes induced by cyclosporine will be investigated. The conscious, chronically instrumented ewe will be used in these experiments. This model avoids the use of anesthesia after the initial instrumentation. Animal will be treated for 2 months with oral cyclosporine to maintain serum levels in the high therapeutic range (400-500ng/ml trough). Renal function studies will be performed before the start of treatment and at one month intervals. Renal functional parameters to be studied include renal blood flow (flow probes), autoregulation of blood flow, inulin and lithium clearance, osmolar clearance, sodium and potassium excretion, excretion rates of n-acetyl-B-glucosaminidase, PGE2, 6-ketoPGF2alpha, thromboxane B2 and plasma renin. Glomerular and tubular morphology will also be studied using light and transmission electron microscopy. Experiment will compare ewes with intact kidneys and those with denervated kidneys in order to determine the relationship of the renal sympathetic nervous system to cyclosporine toxicity. Since alterations in the intrarenal distribution of blood flow may significantly contribute to the pathophysiology of cyclosporine nephrotoxicity, experiments will be performed in which intrarenal blood flow is measured using radioactive microspheres. Renal transplantation remains the most common use for cyclosporine, and because there may be an interaction between cycloporine and other factors influencing early transplant performance, experiments have been designed to study the influence of warm ischemia, cold storage preservation, and renal hypertrophy on the development of cycloporine nephrotoxicity in the transplanted kidney. Finally, because calcium channel blocking cyclosporine immunosuppression, studies of the pharmacokinetic interaction of cyclosporine and verapamil will be examined. In addition, renal function studies after prolonged co-treatment with verapamil and cyclosporine will be performed. The data derived from these experiments will be examined with reference to the basic mechanisms involved in the development of chronic cycloporine nephrotoxicity.